(a) Field of Invention
The present invention relates to an inflatable, reversible liferaft designed to carry several persons and having an integral reserve buoyancy compartment which may be inflated at the discretion of the occupants of said liferaft, for example if the buoyancy of the circumferential buoyancy members or chambers should not be sufficient to support the weight of the occupants and their gear, or if one or more of the above buoyancy members or chambers should become damaged.
(b) Background of the Invention
Inflatable liferafts are known and have been used by mariners for many years, and they are also carried as emergency equipment on board of most aircraft. One of the standard designs for such inflatable liferafts comprises a single circumferential, generally tubular, inflatable buoyancy member or chamber of substantially circular or near-circular, i.e. polygonal, or substantially oval plan to which the floor of said liferaft is tangentially united so as to result in a saucer-like structure. It is evident that such a liferaft is useful only in one position, i.e. with the floor at the bottom and the buoyancy member above said floor. However, it is well known to mariners and airmen alike that it is difficult to launch such a liferaft in bad weather so as to float in the above useful position; that the action of strong winds and waves will often capsize such a liferaft before the passengers have had a chance to board it; and that it is extremely difficult, if not altogether impossible, to right such a capsized liferaft under stormy conditions.
The above considerations and experiences have led to the construction of reversible inflatable rafts having a single circumferential buoyancy member or chamber as described above to which the floor is united along the horizontal mid-line of said buoyancy member or chamber in such a manner as to form a right angle with the tangent of the cross-section of said buoyancy member at said mid-line. However, the use of such types of rafts as lifterafts has not been regarded favourably, because the above method of attachment of the floor to the buoyancy member or chamber creates an area of high stress along the line of juncture when the raft is loaded with passengers which results in comparatively rapid failure of the material in the above area.
The design and construction of reversible inflatable liferafts which is presently preferred comprises two circumferential, inflatable, generally tubular buoyancy members or chambers of substantially circular or near-circular or oval plan shape, both members or chambers of substantially identical dimensions superimposed one upon the other and fixedly united to each other along their line of juncture, with the floor being fixedly and flexibly attached to both buoyancy members or chambers long their line of juncture tangentially to the respective cross-sections of said buoyancy members or chambers at said line of juncture, for example such as described in Silverstone Canadian Pat. No. 675,042, issued Nov. 26, 1963. Such liferafts have the disadvantage of being considerably more expensive than those having a single buoyancy member or chamber, but their design and construction transfers the load exerted upon the floor more evenly to the buoyancy members than in reversible liferafts having a single buoyancy chamber.
However, even the liferafts with two superimposed buoyancy chambers such as briefly described above are known to have failed when exposed to the open sea for prolonged periods of time. The continuous flexing of the material by the action of winds and waves, in addition to the stress exerted upon the floor and upon the buoyancy chambers by the weight of the passengers have been observed to cause cracking and failure of the material to remain air-tight and impervious to water. Under such conditions the liferaft and its occupants may be lost, and it would seem to be advantageous in such an emergency to have some means of reserve buoyancy on board. In this connection it should be noted that none of the presently commercially available types of reversible inflatable liferafts provide means for reserve buoyancy.